docs: def get_urls(self):
          """
          Add ``layout_placeholder_data`` URL.
          """
          # See: `fluent_pages.pagetypes.fluentpage.admin.FluentPageAdmin`.
          urls = super(LayoutAdmin, self).get_urls()
          my_urls = patterns(
              '',
              url(
                  r'^placeholder_data/(?P<id>\d+)/$',
                  self.admin_site.admin_view(self.placeholder_data_view),
                  name='layout_placeholder_data',
              )
          )
          return my_urls + urls